Fix nuget's "Setup SxS dotnet" not being run. (#401)

Author: andykernahan

.github/workflows/nuget.yaml

@@ -26,7 +26,6 @@ jobs:
       with:
         dotnet-version: 3.1.201
     - name: Setup SxS dotnet
-      if: matrix.os == 'windows-latest'
       run: |
         (robocopy %DOTNET_ROOT:3.1.201=2.1.805% %DOTNET_ROOT% /E /XC /XN /XO /NFL /NDL /NJH /NJS /NP) ^& if %ERRORLEVEL% geq 8 exit /B %ERRORLEVEL%
         (robocopy %DOTNET_ROOT:3.1.201=2.1.202% %DOTNET_ROOT% /E /XC /XN /XO /NFL /NDL /NJH /NJS /NP) ^& if %ERRORLEVEL% geq 8 exit /B %ERRORLEVEL%